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A068813
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Primes with a 3 followed by 1's.
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1
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31, 311, 311111, 31111111111, 311111111111, 31111111111111, 31111111111111111111111111111111111, 311111111111111111111111111111111111111111111111, 31111111111111111111111111111111111111111111111111111
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..9.
Makoto Kamada, Prime numbers of the form 311...11.
H. C. Williams, Some primes with interesting digit patterns, Math. Comp. vol 32 no 144 (1978) pp 1306-1310, Table 2, r=3.
Index entries for primes involving repunits
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EXAMPLE
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Digit 3 followed by rep-units of length 1,2,5,10,11,13,34,47,52,77,88,...
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MATHEMATICA
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Select[Table[FromDigits[PadRight[{3}, n, 1]], {n, 2, 100}], PrimeQ] (* Harvey P. Dale, Nov 18 2012 *)
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PROG
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(PARI) for(n=1, 200, if(isprime(3*10^n+(10^(n)-1)/9)==1, print1(3*10^n+(10^(n)-1)/9, ", ")))
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CROSSREFS
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Cf. A002275, A056704.
Sequence in context: A200913 A212235 A126552 * A221306 A142382 A137318
Adjacent sequences: A068810 A068811 A068812 * A068814 A068815 A068816
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KEYWORD
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nonn,base
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AUTHOR
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Amarnath Murthy, Mar 07 2002
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EXTENSIONS
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More terms from Benoit Cloitre, Mar 09 2002
One additional term from Harvey P. Dale, Nov 18 2012
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STATUS
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approved
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